The invention relates to improvements in one-piece rotary material removing tools, especially to improvements in one-piece drills and end milling cutters. More particularly, the invention relates to improvements in one-piece rotary material removing tools which are made of sintered hard metal.
It is already known to extrude sintered hard metal through an orifice which forms an elongated body which is ready to be cooled and to be thereupon converted into a drill or milling cutter. The conversion involves grinding the front end portion of the body to provide one or more cutting edges, grinding or otherwise treating the rear end portion of the body to impart thereto a shape which is suitable for insertion into the socket of a rotary holder, and to provide the body with one or more longitudinally extending chip evacuating grooves. The first step involves the making of a cylindrical blank of sintered material which is thereupon treated in a grinding machine or the like to provide it with one or more cutting edges, one or more grooves, and with a rear end portion which is capable of entering and of being properly retained in a rotary holder. The rear end portion of the blank has a cylindrical shape so that it can be adequately held in a drill chuck. A drawback of such prior proposals is that the cost of the tools is very high, and this is due primarily to the amount of material removing work which is required to form the cutting edge(s) and the chip evacuating groove(s).
A similar one-piece material removing tool is disclosed in German Offenlegungsschrift No. 17 52 616 wherein the chip evacuating groove or grooves are formed without the need for removal of material of the blank in a grinding machine or in a like material removing machine tool. The tool which is disclosed in this publication exhibits the drawback that it does not have any means for supplying coolant to the region where the cutting edge or edges remove material from the workpiece; therefore, the workpiece and/or the tool (especially in the region of the cutting edge or edges) is likely to be overheated after a relatively short interval of use. The rear end portion of the shank of the tool is forced into a cylindrical socket so that the edges bounding the chip evacuating grooves bite into the material of the holder. This creates problems during insertion of the tool into its holder.
German Offenlegungsschrift No. 25 12 854 discloses a further one-piece rotary material removing tool which has a longitudinally extending coolant hole. The body of the tool is a converted extruded hollow cylindrical blank whose cost, prior to conversion into a tool, exceeds the cost of an extruded one-piece tool of sintered hard metal. The cylindrical blank is extruded again in an operation which involves the consumption of large quantities of energy. The rear end portion of the thus treated blank is then soldered or welded to a conical tip which is receivable in the complementary conical socket of a rotary tool holder. Such operation is time-consuming and expensive because the tip is produced as a separate part which is thereupon bonded to the rear end portion of the hollow cylinder. Moreover, it is necessary to provide the tip with a hole which registers with the axial hole of the cylinder in order to ensure admission of coolant by way of the holder. The rear end portion of the hole in the cylinder and/or the passage in the tip is likely to be clogged, either entirely or in part, during welding or soldering of the tip to the cylinder.
One mode of preventing clogging of the coolant hole in a drill is disclosed in German Pat. No. 16 27 778 which proposes to drill one or more coolant holes into the shank of the tool and to weld a conical tip to the rear end portion of the shank. The channel is filled with solder which melts in the course of the welding operation. The cost of such tools is very high because it is necessary to drill one or more coolant holes and to separately produce a tip which is then welded to the rear end portion of the drilled shank. The introduction of solder into the predrilled hole or holes and into the passage or passages of the tip constitutes an additional time-consuming operation and contributes significantly to overall cost of the finished tool.